A NOVEL MUTATION CAUSING COMPLETE THYROID BINDING GLOBULIN DEFICIENCY (TBG-CD MIA) IN A MALE WITH COEXISTING GRAVES DISEASE

ABSTRACT Objective: To report the case of an asymptomatic male diagnosed with Graves disease that, upon further testing, was found to have a complete deficiency of thyroxine-binding globulin (TBG) as the result of a novel frameshift mutation in the TBG (SERPINA7) gene. Methods: The laboratory testing included total thyroxine (T4), free T4 by analog method and direct dialysis, and TBG measurements. Sequencing of genomic DNA was performed using peripheral blood. Results: A 35-year-old East Indian male was referred to endocrinology because of abnormal thyroid function tests (TFTs) done as part of a routine office visit: thyroid-stimulating hormone 0.01 mIU/L (reference range, 0.4 to 3.6 mIU/L) and total T4 3.0 μg/dL (reference range, 5.5 to 10.5 μg/dL). Upon further testing, serum free T4 (2.0 ng/dL; reference range, 0.8 to 1.8 ng/dL) and thyroid-stimulating immunoglobulin (355%; reference, <140%) were elevated and the diagnosis of Graves disease was made. TBG deficiency was suspected because the total T4 co...